You have thought this through very well. I predict great integration success for you. I am excited to ride along with you.I thought some of you might like to know a little more about the chickens' environment.
The yard they forage in is much larger than I'd previously estimated. I measured it to 12m x 6m which is 36m2.
Within the yard is the little prefab coop, providing approximately 2.5m2. It sits on the ground. I've put pavers around its perimeter to keep digging predators at bay. It has a ramp that goes up to a fully enclosed roosting box. The nest box is attached to one end of the roosting box. It's not the Ritz for Chickens but it serves as short term housing for one or two new and small peeps. When it's not used by new ones, the door stays open for all the hens to come and go as they please, which they do every day.
Opening onto the yard, but not within it, is the henhouse. The henhouse is human-sized, I fit in there real easy. It's a mix of Fort Knox and Ritz-Carlton. It's kept the hens safe from many nighttime invasions. I can tell because it's easy for me to see where digging has been attempted. The henhouse has the misting system for hot days and it's furnished with lots of chickeny things to do, like tree stumps for standing on, nest boxes, five feeding stations, water, a ramp up to the first floor. I'm planning to add a second floor soon. The additional floor space and climbing opportunities will be beneficial for all of them as they begin to merge.
The new girls will live in the little coop for a few days. When they're confident in that space, I'll give them some supervised yard time with the big girls enclosed in the henhouse. Once they're confident in the yard, I'll try putting them on the big hens' roost to sleep together, but still be apart during the daytime. Finally, when things are going well, all five can be together all the time.
But I'll have to provide a few hiding spots in the yard, just in case. Spots Janet can't reach. Long, low tunnels, that sort of thing.